In November 2021 I was diving on the HMHS Letitia shipwreck in Halifax Harbour, Nova Scotia, one of Canada’s Maritime provinces. The British hospital ship, which lies near a gray seal colony, ran aground and sank in 1917 while returning from Liverpool, England, with wounded Canadian soldiers.
A few minutes after we started our ascent from the wreck, I saw a giant, tuna-like tail over my shoulder about 20 feet (6 meters) away. Before I could tell what it was, the tail disappeared. When I spotted it again, swimming along the bottom, I immediately recognized the tail of a great white shark before it vanished again. I waved my arms to signal my buddy while not taking my eyes off the spot where the shark had been.
The shark reappeared seconds later to my right, taking a closer look at us. It had circled back inshore, which is a seal-hunting strategy to cut off retreat. There was no question this was a great white — the head shape, chunky body, tapering broad caudal peduncle, high-aspect-ratio tail, and dark dorsal to white counter-shade coloration separated it from the similar but smaller azure mako or porbeagle. With its mouth slightly open, the 11-foot (3.4-m) shark cruised slowly and deliberately past us again and disappeared.
My heart was pounding, and I was in shock and disbelief at being buzzed by a great white late in the season in Halifax Harbour. I started banging my tank with my light to get my buddy’s attention while keeping my head swiveling, watching for the shark.
It appeared a third time up the slope and at the edge of my visibility about 30 feet (9 m) away. It had circled and returned from the same direction, and my buddy finally saw it. We were in murky water with a persistent great white that had made three passes, and we were just a mile from a colony where we regularly saw dead gray seals missing 20-pound (9-kilogram) pieces of meat from their sides and backs. We hugged the seafloor and bottom-crawled back to the ascent line.
Survival mode kicked in when we reached the anchor. We would be vulnerable during our ascent and while silhouetted on the surface before boarding the boat. There would be no safety stop; we went straight to the surface to get out as fast as possible.
When we got to the dive ladder, my buddy laboriously exited, while I stayed in the water and willed him to move faster. Those last few minutes beside the boat felt like the longest in my life as I feared searing, crushing pressure on my lower body and legs. Finally, I flopped onto the deck in an ungainly heap.
After 60 years of swimming in Nova Scotia’s seas, my error was thinking that mid-November was too late for great white sharks to be present near the shore. It should have been no surprise, however, that sharks go by environmental cues, not calendars. The water was an unseasonably warm 54°F (12°C), and seals were abundant nearby.
Great White Presence
To my knowledge, ours was the first open-water diver encounter with a great white shark in Canada. I knew that great whites were present in increasing numbers, having filmed the sharks from a cage in conjunction with Tell Tale Productions, a Halifax documentary production house. We had traveled along Nova Scotia’s eastern coast to film this species underwater for the first time in Canada.
It was surprisingly easy to locate and attract 42 different sharks over four years. On one memorable day we saw seven great whites, including one that was 4.5 feet (1.4 m) long, the youngest that year. Most of the sharks were juveniles under 10 feet (3 m) long.
After getting federal Species at Risk Act permit clearance, we used tuna heads, drones, pole cameras, remote feed cameras, a Gemini wide-beam sonar, and me in a cage to film them from an anchored boat well away from other humans. The first underwater images of this species in Canada were the back cover illustration of my 2022 guidebook, Maritime Marine Life, and the overall effort led to the first Discovery USA Shark Week documentary shot in Canada, Great White North, in 2024.
Population Increase
Research reveals that the most significant impact on great white sharks in the Northwest Atlantic after World War II was trophy fishers in New England capturing them, which removed the most fecund animals. While this practice is no longer permitted, the damage to a slow-growing, long-lived species was done, and accurate population estimates remain elusive.
In 2018 a prominent Canadian researcher modeled an estimate of the entire Northwest Atlantic great white population at 500 animals. Recent telemetry studies by Greg Skomal, PhD, show a population of at least 800 near Cape Cod, Massachusetts. Multiple thousands of great whites is a reasonable guess for the entire North Atlantic. It appears that many sharks make a seasonal northward migration into seal-rich Canadian waters, going as far as the Gulf of St. Lawrence and Newfoundland to forage.
Human and Shark Coexistence
Evidence suggests that great white sharks have special brains with very strong receptors and huge olfactory, acoustic, and optical tracts and lobes. Like most shark species, they are not as strong at processing information. While fewer humans may be viewing great whites as dangerous predators, we still need to realize how their brains govern their behavior.
Great whites have evolved over 30 million years as ambush predators of mammals. We can’t count on them to use a central processing brain segment the size of a walnut to distinguish divers from seals while charging in bad visibility during a full-on attack. Over the past five years, my field observations using remote cameras to watch shark populations naïve about humans have revealed that no two animals behave the same while approaching food. There are bold 10-foot (3-m) sharks, often covered in scars from seal scratches, who charge in and seize baits. I have also seen less-beat-up, cautious sharks spend 20 minutes doing dozens of ever-diminishing circles and passes before they slowly bump and eventually cautiously nibble a hanging bait.
Sharing the inshore zone in the Maritime provinces of Canada and the Northeastern U.S. with white sharks for the foreseeable future is a new situation for locals. After a serious swimmer attack in Nova Scotia in 2021 and an unprecedented fatality in Maine in 2020, people are trying to develop a better sense of how to interact with a mighty ocean predator in waters where caution has not been required before.
With the extensive food supply in the northern Atlantic and warming waters elsewhere, great white sharks are here for the long haul. People in the ocean — surfers, swimmers, kayakers, stand-up paddleboarders, and divers — are now in a great white environment. While the risk of an encounter is low, it is not absent.
Situational awareness is crucial to sharing waters with great whites, and we have to be vigilant and react appropriately. In addition to all the other well-worn shark safety tropes, pay close attention to the marine life around you. If seals are behaving abnormally — such as climbing vertical cliffs to get out of the sea, climbing into your boat or onto your surfboard, or swimming where they don’t normally go, such as inshore from a surf break — go somewhere else. It’s safer to stay out of the water entirely if seals are around, especially if your apparel makes you look like them. Finding these safer areas is a major challenge in the murky Canadian Maritimes, where there are thousands of gray seals.
Reading a recent account of a seasoned diver’s bucket list moment — their delight at seeing a large great white while diving off Catalina Island in California — I wish I could share their breathless enthusiasm. How lyrical the diver’s description made the shark’s presence sound, highlighting its sleek and deadly beauty as it ghosted past.
The reality of my encounter was that I felt hunted in a way I hadn’t before in hundreds of other shark encounters over 47 years of research, more than 50 underwater film documentaries, and more than 3,000 dives. I was not mentally prepared for the encounter on that early winter day, but the changes in our ecosystem mean we will need to expect great whites where we have not seen them before.
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© Alert Diver – Q1 2025